Driver drill

BACKGROUND OF THE INVENTION

0001This application claims the benefit of Japanese Patent Application Number 2004-4610 filed Jan. 9, 2004, the entirety of which is incorporated by reference.

00021. Field of the Invention

0003The present invention relates to a driver drill usable with a selection of a clutch mode and a drill mode.

00042. Description of the Related Art

0005In a driver drill, firstly, a clutch mode is achieved in a planetary gear reduction mechanism disposed between a motor and a spindle with a structure in which one of internal gears interlocked with the circumference of planetary gears can be rotated within a housing. Also, the internal gear is pressed and locked by a coil spring through steel balls held by a gear case accommodating the planetary gear reduction mechanism and engaged with an end face of the internal gear and through a washer externally provided to the gear case so as to abut on the steel balls. That is, when a load on the spindle is increased to exceed a biasing force of the coil spring, the internal gear idles to interrupt the transfer of rotation to the spindle.

0006On the other hand, a drill mode is achieved by a locking means that makes a spring holder for holding the coil spring or another pressing member directly abut on the washer disposed between the steel ball and the coil spring by rotative operation of an operating member, such as a change ring, thereby regulating the movement of the washer. However, as tolerances of the components, such as the washer and the pressing member, is increasingly accumulated, the washer might move to operate the clutch even in the drill mode. To solve this problem, in a clutch mechanism disclosed in Japan Published Unexamined Patent Application No. 9-79292, protrusions are provided so as to abut on the outer circumference of the washer and an inner surface of a cap as an operating member. According to this mechanism, when the drill mode is selected, the protrusions of the cap ride on the protrusions of the washer, thereby regulating the movement of the washer without a spring holder.

0007However, the clutch mechanism disclosed in the above patent document is designed to regulate the movement of the washer externally provided to the housing by using a cap, which is a member separated from the housing. Therefore, even with the clutch mechanism, an influence of the tolerances of the housing and the cap cannot be eliminated. After all, the possibility of the occurrence of erroneous operation of the clutch in the drill mode cannot be prevented.

SUMMARY OF THE INVENTION

0008Therefore, an object of the present invention according to a first aspect is to provide a driver drill that can effectively prevent erroneous clutch operation in a drill mode and can achieve excellent reliability.

0009To achieve the object mentioned above, in the first aspect of the present invention, a locking means for regulating the movement of an intermediate member, such as a washer, serves as an interfering unit provided with a gear case to interfere with the intermediate member at a predetermined rotating position of the intermediate member to regulate the movement, and the rotative operation of the operating member enables the intermediate member to rotate to a lock position where interference occurs with the interfering unit and to a lock-releasing position where no interference occurs with the same, thereby allowing the clutch mode and the drill mode to be selected.

0010In a second aspect of the present invention based on the first aspect, the driver drill further includes a cam means that can add percussion operation to an axial direction in conjunction with the spindle. In order to achieve excellent operability associated with selection of the operation mode, the operating member has a third rotating position other than rotating positions in the clutch mode and the drill mode, where the cam means is in conjunction with the spindle and the intermediate member interferes with the interfering unit. Then, by rotative operation of the operating member, a percussion mode in which percussion is transferred to the spindle can be further selected.

0011In a third aspect of the present invention based on the first or second aspect, in order to reliably perform torque adjustment and switching the operation mode in the clutch mode, the driver drill further includes a second operating member capable of adjusting a pressing force of the pressing means by rotative operation.

0012According to the first aspect of the present invention, the movement of the intermediate member is regulated by the interfering unit provided with the gear case which holds the intermediate member. Due to this, the intermediate member is securely locked without being influenced by tolerances among the components. Therefore, erroneous clutch operation in a drill mode can be effectively prevented, and excellent reliability can be achieved.

0013According to the second aspect of the present invention, in addition to the effect of the first aspect, any one of three operation modes, that is, the clutch mode, drill mode, and the percussion mode, can be selected only by rotative operation of the operating member. Therefore, outstanding usability can be achieved.

0014According to the third aspect of the present invention, in addition to the effect of the first or second aspect, torque adjustment in the clutch mode is performed by the second operating means, which is provided separately from the operating member. Therefore, switching of the operation mode can be performed irrespective of the position where torque adjustment is performed by the second operating member. Furthermore, the operation mode is prevented from being erroneously switched at the time of torque adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

0015<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of a percussion driver drill.

0016<figref idref="DRAWINGS">FIG. 2</figref> is a vertical section view of the percussion driver drill.

0017<figref idref="DRAWINGS">FIG. 3</figref> is an exploded perspective view of a gear assembly.

0018<figref idref="DRAWINGS">FIGS. 4A and 4B</figref> are vertical section views of the gear assembly in a clutch mode.

0019<figref idref="DRAWINGS">FIG. 4C</figref> is a section view taken along line A—A shown in <figref idref="DRAWINGS">FIG. 4B</figref>.

0020<figref idref="DRAWINGS">FIG. 5A</figref> shows a side view and a section view taken along line B—B of a second gear case.

0021<figref idref="DRAWINGS">FIG. 5B</figref> is an illustration for describing a flat washer.

0022<figref idref="DRAWINGS">FIG. 5C</figref> is an illustration for describing a mode-change ring.

0023<figref idref="DRAWINGS">FIG. 6</figref> shows a side view and a section view taken along line C—C of the second gear case with the mode-change ring attached thereto.

0024<figref idref="DRAWINGS">FIGS. 7A and 7B</figref> are vertical section views of the gear assembly in a drill mode.

0025<figref idref="DRAWINGS">FIG. 7C</figref> is a section view taken along line D—D shown in <figref idref="DRAWINGS">FIG. 7B</figref>.

0026<figref idref="DRAWINGS">FIGS. 8A and 8B</figref> are vertical section views of the gear assembly in a percussion mode.

0027<figref idref="DRAWINGS">FIG. 8C</figref> is a section view taken along line E—E shown in <figref idref="DRAWINGS">FIG. 8B</figref>.

DETAILED DESCRIPTION OF THE PREFERRED EMBODDIMENTS

0028An embodiment according to the present invention is described below based on the drawings.

0029<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of a percussion driver drill, which is an example of a driver drill, and <figref idref="DRAWINGS">FIG. 2</figref> is a vertical section view of the percussion driver drill. A percussion driver drill <b>1</b> has a motor <b>3</b> accommodated in a body housing <b>2</b> formed of a pair of right and left half-housings. From an output shaft <b>4</b> of the motor <b>3</b>, rotation is transferred to a spindle <b>5</b> through a gear assembly <b>7</b> mounted at the front side (at the right in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>) in the body housing <b>2</b> and from which the spindle <b>5</b> protrudes forward. At the front end of the spindle <b>5</b>, a drill chuck <b>6</b> whose tip can hold a bit is provided. The reference number <b>8</b> denotes a switch for driving the motor <b>3</b>, and the reference number <b>9</b> denotes a handle. Moreover, the reference number <b>10</b> denotes a battery pack as a power source mounted at the lower end of the handle <b>9</b>.

0030As shown in <figref idref="DRAWINGS">FIGS. 3 and 4</figref>, the gear assembly <b>7</b> includes a first gear case <b>11</b> and a second gear case <b>12</b> mounted at the front of the first gear case <b>11</b>. As shown in <figref idref="DRAWINGS">FIG. 5A</figref>, the second gear case <b>12</b> has a two-step cylindrical shape with a large-diameter unit <b>13</b> and a small-diameter unit <b>14</b>. A known planetary gear reduction mechanism is accommodated inside the first gear case <b>11</b> and the large-diameter unit <b>13</b>. In the planetary gear reduction mechanism, a plurality of planetary gears <b>15</b>, <b>15</b> . . . , carriers <b>16</b>, <b>16</b> . . . supporting the same and internal gears <b>17</b>, <b>17</b> . . . interlocked with the outer circumference of the planetary gears <b>15</b>, <b>15</b> . . . are disposed in three layers. The spindle <b>5</b> is spline-connected at its rear end to a lock cam <b>18</b> which is integrally formed with the carrier <b>16</b> of the third layer. The spindle <b>5</b> is also axially supported by ball bearings <b>19</b> and <b>20</b> in the small-diameter unit <b>14</b> of the second gear case <b>12</b>. Therefore, the spindle <b>5</b> receives the reduced speed of rotation of the output shaft <b>4</b>, and also can move back and forth in an axial direction.

0031In a normal state, the spindle <b>5</b> is pressed toward a forward position where a first cam <b>26</b> (which will be described below) abuts on the ball bearing <b>20</b>. The spindle is pressed by a flange <b>21</b> formed at the front side and a coil spring <b>22</b> externally mounted between the flange <b>21</b> and the ball bearing <b>20</b>. The reference numbers <b>23</b> and <b>24</b> denote cylindrical spacers, inserted from the front side to the inner circumference of the small-diameter unit <b>14</b> for clipping and positioning the ball bearing <b>20</b>. The reference number <b>25</b> denotes a disk-shaped stopper plate screwed to the front end of the small-diameter unit <b>14</b> for preventing the spacer <b>24</b> from coming off.

0032Also, between the ball bearings <b>19</b> and <b>20</b> around the spindle <b>5</b>, a first cam <b>26</b> and a second cam <b>27</b> each having a ring shape are externally and coaxially mounted from the front side. The first cam <b>26</b> has first cam gears <b>28</b>, <b>28</b> . . . on its rear surface, radially and continuously formed in a circumferential direction. The first cam is also integrally fixed to the spindle <b>5</b> inside the spacer <b>23</b>. The second cam <b>27</b> has second cam gears <b>29</b>, <b>29</b> . . . each having the same shape as the first cam gears <b>28</b>, <b>28</b> . . . on its front surface facing to the first cam gears <b>28</b>, <b>28</b> . . . . Moreover, the second cam <b>27</b> has a spline portion <b>30</b> on its outer circumference of its rear surface. The second cam <b>27</b> is slipped onto the spindle <b>5</b> with play, so that it can move back and forth in a rotational and axial direction. In a forward direction, the second cam <b>27</b> can only slightly move until a position where the second cam <b>27</b> is interlocked with the first cam <b>26</b>. In a backward direction, the second cam <b>27</b> is regulated by a stopper <b>31</b> protruding toward the inner circumference of the small-diameter unit <b>14</b>, and can slightly move until a position where the second cam <b>27</b> abuts on a pair of washers <b>33</b> holding a plurality of steel balls <b>32</b>, <b>32</b> . . . .

0033Furthermore, the small-diameter unit <b>14</b> is formed with guide grooves <b>34</b>, <b>34</b> . . . extending from its front end along the axial direction to be symmetrical to the point. In each of the guide grooves <b>34</b>, a coil spring <b>35</b> and a percussion switching lever <b>36</b> are slidably provided. On an inner surface of the rear end of each percussion switching lever <b>36</b>, an inner protrusion <b>37</b> is provided protruding toward the inner circumference of the small-diameter unit <b>14</b> so as to be interlockable with the spline portion <b>30</b> of the second cam <b>27</b> at a forward position. Also, on an outer surface of the front end of each percussion switching lever <b>36</b>, an outer protrusion <b>38</b> is provided protruding toward the outer circumference of the small-diameter unit <b>14</b>.

0034On the other hand, around the small-diameter unit <b>14</b>, a mode-change ring <b>39</b> as an operating member is rotatably mounted between the front end of the body housing <b>2</b> and the stopper plate <b>25</b>. The mode-change ring <b>39</b> includes an operation ring <b>40</b>, a cam ring <b>41</b> and three connecting plates <b>42</b>, <b>42</b> . . . . While the operation ring <b>40</b> has a diameter approximately equal to that of the front end of the body housing <b>2</b>, the cam ring <b>41</b> has a diameter smaller than that of the operation ring <b>40</b> and is positioned at the front thereof. The three connecting plates <b>42</b>, <b>42</b> . . . extend from the outer circumference of the cam ring <b>41</b> in the axial direction and are uniformly spaced apart in a circumferential direction for connecting both the rings <b>40</b> and <b>41</b>. The cam ring <b>41</b> of this mode-change ring <b>39</b> abuts on the outer protrusion <b>38</b> of the percussion switching lever <b>36</b> at its rear-end edge. This configuration makes it possible to regulate the forward position of the percussion switching lever <b>36</b> pressed forward by the coil spring <b>35</b>. Also, a pair of cam concave portions <b>43</b>, <b>43</b> are provided, each having a trapezoidal shape and being symmetrical to the point, at the rear-end edge of the cam ring <b>41</b>. When the mode-change ring <b>39</b> is at a rotating position where the cam concave portions <b>43</b> are positioned in front of the outer protrusion <b>38</b>, the percussion switching lever <b>36</b> goes forward to allow the inner protrusion <b>37</b> to be engaged with the spline portion <b>30</b> of the second cam <b>27</b>. Furthermore, when the mode-change ring <b>39</b> is at a rotating position where the cam concave portions <b>43</b> are not positioned in front of the outer protrusion <b>38</b>, the percussion switching lever <b>36</b> goes backward to allow the inner protrusion <b>37</b> to be disengaged from the spline portion <b>30</b> of the second cam <b>27</b>.

0035The reference number <b>44</b> denotes a cylindrical change ring as a second operating member externally and rotatably mounted around the mode-change ring <b>39</b> between the front side of the operation ring <b>40</b> and the stopper plate <b>25</b>. An internal screw portion <b>45</b> is provided in the inner circumference of the change ring <b>44</b>. Around the small-diameter unit <b>14</b>, a spring holder <b>46</b> is provided so as to move in the axial direction. In the spring holder <b>46</b>, an external screw portion <b>47</b> protrudes from the connecting plates <b>42</b>, <b>42</b> . . . of the mode-change ring <b>39</b> to be screwed into the internal screw portion <b>45</b> of the change ring <b>44</b>. Therefore, when the mode-change ring <b>39</b> is rotated, the spring holder <b>46</b> is screwed toward in the axial direction.

0036On the other hand, as shown in <figref idref="DRAWINGS">FIG. 5B</figref>, around the bottom of the small-diameter unit <b>14</b>, a flat washer <b>48</b> is provided as an intermediate member. The flat washer <b>48</b> has three external projections <b>49</b>, <b>49</b> . . . protruding from an edge of the outer circumference of the small-diameter unit <b>14</b> and uniformly spaced apart in a circumferential direction, and also has four internal projections <b>50</b>, <b>50</b> . . . protruding from an edge of the inner circumference thereof and forming two pairs with bilateral symmetry. As shown in <figref idref="DRAWINGS">FIG. 5C</figref> and <figref idref="DRAWINGS">FIG. 6</figref>, the external projections <b>49</b>, <b>49</b> . . . fit in concave grooves <b>51</b>, <b>51</b> . . . provided in the axial direction to the inner circumference of the operation ring <b>40</b> of the mode-change ring <b>39</b>, and are rotatable integrally with the mode-change ring <b>39</b> and movable separately in the axial direction. As shown in <figref idref="DRAWINGS">FIG. 5A</figref>, protruding streaks <b>52</b>, <b>52</b> . . . as interfering units are provided along the axial direction on the outer circumference of the small-diameter unit <b>14</b>. The protruding streaks <b>52</b>, <b>52</b> . . . are formed on a front side of the small-diameter <b>14</b> having a distance of the approximate thickness of the flat washer <b>48</b> from the front surface of the large-diameter unit <b>13</b>. A part of the protruding streaks <b>52</b>, <b>52</b> . . . coincides with a shape of the inner circumference of the flat washer <b>48</b> and the remaining part of the same rides on the internal projections <b>50</b>, <b>50</b> . . . in the axial direction. Therefore, the flat washer <b>48</b> can rotate at the bottom of the small-diameter unit <b>14</b> where the protruding streaks <b>52</b> are not provided (at a backward position, which will be described further below). On the other hand, the flat washer <b>48</b> can move forward from that bottom only at a coinciding position (a lock-releasing position) shown in <figref idref="DRAWINGS">FIG. 6</figref> where the internal projections <b>50</b> do not interfere with the protruding streaks <b>52</b> in the axial direction.

0037Between the flat washer <b>48</b> and the spring holder <b>46</b>, a coil spring <b>53</b> serving as a pressing means is externally mounted around the small-diameter unit <b>14</b> to press the flat washer <b>48</b> toward the large-diameter unit <b>13</b>. Inside the large-diameter unit <b>13</b> at the rear of the flat washer <b>48</b>, sets of two steel balls <b>54</b>, <b>54</b> . . . aligned back and forth are provided as engaging members. The steel balls <b>54</b>, <b>54</b> . . . are uniformly spaced apart and held in the circumferential direction. With this configuration, the steel balls <b>54</b>, <b>54</b> . . . can abut on the front surface of the internal gear <b>17</b> rotatably provided to the third layer of the planetary gear reduction mechanism, and can be engaged in the circumferential direction with clutch cams <b>55</b>, <b>55</b> . . . . Each of the clutch cams <b>55</b>, <b>55</b> . . . has a trapezoidal shape, and it protrudes from the front surface of the internal gear <b>17</b> to the circumferential direction and are uniformly spaced apart. Through these steel balls <b>54</b>, <b>54</b> . . . and the flat washer <b>48</b>, a biasing force of the coil spring <b>53</b> is directly transferred to the internal gear <b>17</b>. Therefore, rotation of the internal gear <b>17</b> is regulated by the biasing force of the coil spring <b>53</b>. Also, as the spring holder <b>46</b> is screwed in accordance with the rotative operation of the change ring <b>44</b>, the length of the coil spring <b>53</b> in the axial direction is changed, thereby allowing the biasing force to the internal gear <b>17</b> to be changed. Here, in this pressing state, the flat washer <b>48</b> is at the backward position which is close to, but does not allow the flat washer <b>48</b> to make contact with, the front surface of the large-diameter unit <b>13</b>.

0038In the above-structured percussion driver drill <b>1</b>, as will be described in the following, any one of three operation modes can be selected based on the rotating position of the mode-change ring <b>39</b> accompanied by back-and-forth movement of the percussion switching lever <b>36</b> and the rotation of the flat washer <b>48</b>.

0039Firstly, as shown in <figref idref="DRAWINGS">FIG. 4C</figref>, in a first rotating position of the mode-change ring <b>39</b> at which the internal projections <b>50</b> of the flat washer <b>48</b> do not interfere with the protruding streaks <b>52</b> of the small-diameter unit <b>14</b> in the axial direction, the cam concave portions <b>43</b> of the cam ring <b>41</b> are positioned away from the front of the percussion switching lever <b>36</b>. Therefore, as shown in <figref idref="DRAWINGS">FIG. 4A</figref>, the percussion switching lever <b>36</b> is at a backward position, and thus the inner protrusion <b>37</b> and the second cam <b>27</b> are not connected to each other. Accordingly, in a condition that the second cam <b>27</b> is freely rotatable and that the flat washer <b>48</b> is movable forward, rotative operation of the change ring <b>44</b> leads to a clutch mode, in which the pressing force to the flat washer <b>48</b> can be changed.

0040In this clutch mode, when the motor <b>3</b> is driven to rotate the spindle <b>5</b>, screwing or the like can be performed with the driver bit mounted on the drill chuck <b>6</b>. When screwing proceeds to a state in which a load on the spindle <b>5</b> exceeds the pressing force of the coil spring <b>53</b> locking the internal gear <b>17</b>, the clutch cams <b>55</b>, <b>55</b> . . . of the internal gear <b>17</b> push the steel balls <b>54</b>, <b>54</b> . . . as well as the flat washer <b>48</b> forward to allow the internal gear <b>17</b> to idle, thereby ending screwing (clutch is operated). Here, as the driver bit is pressed toward a screw, the spindle <b>5</b> moves backward to allow the first cam <b>26</b> and the second cam <b>27</b> to be interlocked with each other. However, since the second cam <b>27</b> is freely rotatable, the second cam <b>27</b> rotates together with the first cam <b>26</b>, and therefore percussion does not occur to the spindle <b>5</b>.

0041Next, as shown in <figref idref="DRAWINGS">FIGS. 7A to 7C</figref>, in a second rotating position where the mode-change ring <b>39</b> is rotated by 30 degrees to the left from the position in the clutch mode, the cam concave portions <b>43</b> of the cam ring <b>41</b> are not yet positioned in front of the percussion switching lever <b>36</b>, and the percussion switching lever <b>36</b> is still at the backward position. At this time, the flat washer <b>48</b> rotates as shown in <figref idref="DRAWINGS">FIG. 7C</figref> to enable the internal projections <b>50</b> to move to a position behind the protruding streaks <b>52</b> of the small-diameter unit <b>14</b> (a locked position). This leads to a drill mode, in which the forward movement of the flat washer <b>48</b> is always regulated by the protruding streaks <b>52</b> irrespective of the pressing force of the coil spring <b>53</b>.

0042When the spindle <b>5</b> is rotated in this drill mode, the steel balls <b>54</b>, <b>54</b> . . . never go over the clutch cams <b>55</b> of the internal gear <b>17</b> irrespective of the load on the spindle <b>5</b>. Therefore, the internal gear <b>17</b> is still locked, and the spindle <b>5</b> continues to rotate. Here, also at this time, the second cam <b>27</b> is still freely rotatable, and therefore percussion does not occur to the spindle <b>5</b>.

0043Then, as shown in <figref idref="DRAWINGS">FIGS. 8A to 8C</figref>, in a third rotating position where the mode-change ring <b>39</b> is further rotated by 30 degrees to the left from the position in the drill mode, the cam concave portions <b>43</b> of the cam ring <b>41</b> are positioned in front of the percussion switching lever <b>36</b>, allowing the percussion switching lever <b>36</b> to move forward so as to connect the inner protrusion <b>37</b> to the second cam <b>27</b>. On the other hand, interference in the axial direction between the inner protrusion <b>50</b> of the flat washer <b>48</b> and the protruding streaks <b>52</b> of the small-diameter unit <b>14</b> is not changed. This leads to a percussion mode, in which the first cam <b>26</b> and the second cam <b>27</b> are interlocked with each other at the backward position of the spindle <b>5</b>.

0044When the spindle <b>5</b> is rotated in this percussion mode, the spindle <b>5</b> is moved backward by pressing the drill bit or the like onto a material to be processed. Then, the first cam <b>26</b> rotating integrally with the spindle <b>5</b> interlocks with the second cam <b>27</b> which is locked by the percussion switching lever <b>36</b>, whereby percussion occurs to the spindle <b>5</b>. Here, as the flat washer <b>48</b> is still locked by the protruding streaks <b>52</b>, the spindle <b>5</b> continues to rotate irrespective of the load on the spindle <b>5</b>.

0045A leaf spring <b>56</b> is fixed to the inner circumference at the front end of the body housing <b>2</b>. On the other hand, as shown in <figref idref="DRAWINGS">FIG. 5C</figref> and <figref idref="DRAWINGS">FIG. 6</figref>, three concave portions <b>57</b>, <b>57</b> . . . are provided around the outer circumference at the rear end of the operation ring <b>40</b> in the mode-change ring <b>39</b>. The leaf spring <b>56</b> is engaged with each of the concave portions <b>57</b> at a rotating position corresponding to the relevant mode. In this way, click operation can be achieved for positioning the mode-change ring <b>39</b> in the relevant mode.

0046As described above, according to the percussion driver drill <b>1</b> in the embodiment described above, the protruding streaks <b>52</b> serve as the locking means for locking the flat washer <b>48</b>. The protruding streaks are provided on the small-diameter unit <b>14</b> of the second gear case <b>12</b> to interfere with the flat washer <b>48</b> at a predetermined rotating position of the same to regulate its movement. By rotative operation of the mode-change ring <b>39</b>, the flat washer <b>48</b> is rotated to a lock position where interference occurs with the protruding streaks <b>52</b> and to a lock-releasing position where interference does not occur with the protruding streaks <b>52</b>. This allows either the clutch mode or the drill mode to be selected. Therefore, the flat washer <b>48</b> can be securely locked without being influenced by tolerances among the components. Due to this, erroneous clutch operation in the drill mode can be effectively prevented, and high reliability can be achieved.

0047Also, in the above embodiment, the mode-change ring <b>39</b> has a third rotating position other than rotating positions in the clutch mode and the drill mode, where the second cam <b>27</b> is locked by the percussion switching lever <b>36</b> and the front washer <b>48</b> interferes with the protruding streaks <b>52</b>. With this configuration, by rotative operation of the mode-change ring <b>39</b>, the percussion mode can be selected for the spindle <b>5</b>. Therefore, any one of three operation modes, that is, the clutch mode, drill mode, and the percussion mode, can be selected only with the rotative operation of the mode-change ring <b>39</b>, whereby outstanding usability is achieved.

0048Furthermore, in the above embodiment, the change ring <b>44</b> is provided for torque adjustment in the clutch mode, separately from the mode-change ring <b>39</b>. Therefore, switching of the operation mode can be performed irrespective of the position where torque adjustment is performed by the change ring <b>44</b>. Still further, the operation mode is prevented from being erroneously switched at the time of torque adjustment.

0049Here, in the above embodiment, the protruding streaks are provided with the small-diameter unit in the axial direction of the second gear case in order to regulate the movement of the flat washer. Alternatively, another interference unit, such as protruding streaks or pin-shaped protrusions provided in a circumferential direction, can regulate the movement of the flat washer. Also, the intermediate member is not restricted to the flat washer, but may be a cylindrical body. Furthermore, the engaging members are not restricted to the steel balls, and pins with their end being shaped like a cylinder or circle can be adopted.

0050Still further, the above embodiment is described with a percussion driver drill in which a percussion mode is selectable. However, a locking means similar to that in the above embodiment can be adopted for a driver drill not having a cam means and a percussion mode. Also, the present invention can be applied to even a driver drill or a percussion driver drill in which operation-mode selection and torque adjustment can be performed only with a single operating member.